Statistical data show that from 1984 to 1993 40,000 roads accidents took place only in Italy, in which 4,000 people were injured and 200 people died, due to animals crossing roads, especially abandoned dogs. Only in the area comprising the province of Turin, Italy, in the second half of 2001 there were 157 accidents due to wild animals crossing roads, in particular wild boars, but also roes, foxes, stags and badgers.
In general in Europe the number of accidents involving animals and vehicles, considering only large mammals, has been calculated to be of 507,000, with 100 deaths, 30,000 injured people and damages for about 1,000,000 Euro. The corresponding figure for each Italian province is of about 100 accidents every year.
Similarly alarming statistics come from the United States, especially as far as accidents involving stags are concerned. Every year there are 726,000 accidents with said animals in the United States, with subsequent damages for about 1,000,000 dollars. Always every year 29,000 people are injured and 200 people die in the United States due to this kind of accidents.
In the light of solving this problem several solutions have already been suggested, all of which propose the use of ultrasounds so as to keep the animal away from the area in which vehicles travel. Such a solution includes the so-called “wild life warning system” marketed by International Road Dynamics Inc., which achieves its objective by installing systems detecting the passage of vehicles and ultrasound emitters in stationary positions, typically in the areas where statistically animal crossing is most frequent. The sensors detect the arrival of a vehicle and thus activate ultrasound emitters, and—if necessary—light bands and/or scent emitters which frighten the animals and prevent the latter from crossing the road. The first system to be activated leads to the activation of the following ones on both road sides.
Ultrasound emission is an excellent system to make the animal get away, without simultaneously disturbing humans. Animals generally have a sound sensitive threshold that is far higher that humans. They can hear sounds having a lower intensity with respect to human ear. For instance, while the audible range for humans is of 64 to 23,000 Hz, the corresponding range for dogs is of 67–45,000 Hz, for cats of 45–64,000 Hz, for cows of 23–35,000, for sheep of 100–30,000 Hz, for rabbits of 360–42,000 Hz. Scientific researches have shown that generating sounds within the critical perceptible range a lot of animals feel so much disturbed and threatened to get away from sound source. At the same time humans are not disturbed by ultrasounds, which belong to a frequency range beyond human audible threshold. In humans the eardrum has a far lower specific resonance frequency than animals, and cannot therefore vibrate at ultrasound frequency. Human ear can perceive sounds up to a frequency of 20,000 Hz.
Considering the above, on-board devices to be installed on a vehicle have also been used to keep away animals crossing the road before said vehicle. For instance U.S. Pat. No. 5,278,537 discloses an electronic alarm system that generates ultrasounds to prevent animals from moving before the vehicle. Said device includes a simplified pilot circuit generating electric pulses in form of square waves having constant peak-to-peak tensions. The pilot circuit generates said square waves with sequentially increasing periodical wave frequencies followed by sequentially decreasing wave frequencies. A coupling transformer converts square waves into sinusoidal wave electric tensions having high peak-to-peak tensions, so that a piezoelectric transducer emits ultrasounds with periodically increasing frequencies followed by periodically decreasing frequencies, thus simulating the effect of a siren, without overheating the transducer and causing its premature breaking. The ultrasonic effect thus obtained confounds the animal and prevents the latter from suddenly crossing the road before the vehicle.